johnf wrote:
> In a many to many relationship there is often a third table -intermediary
> table. Normally, I link based on two fields. But bizobj.LinkField only
> allows one string or one field. It would be nice if the bizobj.LinkField
> could accept a tuple with multi fields and have the where cause work
> correctly for the child.
>
> So it would be nice to have a bizobj.LinkField that accepted more than just
> one field.
>
> Of course there maybe a different way to handle the situation of needing a
> where clause that requires to fields.
What I do is define a base bizobj for the intermediary table, and then make 2
subclasses, one for each parent. For example, with a people table and a
categories
table, where each person can be a member of any number of categories:
create table people (id integer primary key,
name char);
create table categories (id integer primary key,
name char);
create table peoplecat (id integer primary key,
person_id,
category_id);
The peoplecat table is the intermediary table. So I make a bizobj on the
peoplecat
table, with SQL like:
select peoplecat.id as id,
peoplecat.person_id as person_id,
peoplecat.category_id as category_id,
people.name as person_name,
categories.name as category_name
left join people
on people.id = peoplecat.person_id
left join categories
on categories.id = peoplecat.category_id
group by peoplecat.id
I then make 2 subclasses, PeopleForCategory and CategoriesForPerson.
PeopleForCategory has a LinkField of category_id, and CategoriesForPerson has a
LinkField of person_id.
Your People bizobj adds CategoriesForPerson as a child, and your Categories
bizobj
adds PeopleForCategory as a child.
Your UI then uses a grid to display the child records, and you write code to
add more
categories/people links, or to delete existing links. That code should mostly
go in
the base bizobj class for the intermediary bizobj.
I find this works very well. Not sure if we can really put something in the
framework
to handle this automatically...
Paul
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